Atomic magnetometers use measurements of electron spin precession frequency to achieve high sensitivity to magnetic fields. I will describe recent advances in the precision of these measurements that allow us to measure very small fields and enable new applications, such as detection of magnetic fields generated by the brain. Atomic magnetometers are also sensitive to new types of spin interactions, for example, symmetry breaking due to violation of local Lorentz invariance. To search for such effects, we have installed a sensitive magnetometer at the South Pole, which is a preferred location for such experiments due to alignment of Earth's rotation and gravity directions.